Heat and solvent sealable polyolefin films



United States Patent ABSTRACT OF THE DISCLOSURE Non-blocking, heat and solvent scalable polyolefin films can be produced by coating polyolefin substrates with a blend of copolymers of a (a) ethylene/vinyl acetate and (b) ethylene/ ethyl acrylate;

said copolymers being present in the blend in weight ratios, respectively of from about 0.3 to 1 to about 1 to 0.7.

This invention relates to polyolefin films that are both heat and solvent scalable. More particularly, this invention relates to polyolefin films coated with a blend of copolymers of which ethylene is the major component.

Films of a thickness of the order of from about 0.5 mil to about mils prepared from polyolefin resins such as polyethylene or polypropylene have Widespread utility as packaging materials. The heat and solvent sealing properties of such polyolefin films (in the absence of special coatings) have not been entirely satisfactory for various reasons. For example, in attempting to heat seal polyolefin films, per se, the relativelyhigh temperatures required to effect a satisfactory heat seal tend to cause distortion and wrinkling of the films, while satisfactory solvent sealing of polyolefin films, per se, is practically impossible with *most common solvents.

Certain materials have been suggested heretofore to solve specific problems such as the heat-sealing problem or the solvent-sealing problem. For example, copolymers of ethylene/vinyl acetate have been suggested for solvent sealing. However, these materials tend to bloek'to an undesirable degree in automatic packaging machinery. In another example, copolymers of ethylene/ethyl acrylate are satisfactory for heat scaling in automatic packaging machinery, but are not suitable for solvent sealing applications. I I c It has now been discovered that certain blends of the aforesaid copolymers are not only adaptable to both solvent and heat-sealing processes, but'also overcome the tendency to block in automatic packaging machinery mentioned above. Thus, the present invention comprises a heat-scalable polyolefin film adapted particularly for use as a packaging and wrapping material for food products, tobacco products, confectionery "products and the like, which film contains on at least one surface thereof, a coating consisting essentially of a blend of V (a) a copolymer of ethylene/vinyl acetateiand (-b) a copolymer of ethylene/ethyl acrylate,

the weight ratio of (a) to (b) in said blend being, respectively, from about 0.3 to 1 to about 1 to 0.7 (preferably from about 0.5 :1 to about 1.121). The copolymerv blend coatings of the present invention are relatively thin, generallyhaving a thickness of at mostabout 3 mils and preferably having a thickness of from about 0.1 to about 1.5 mils.

Polyolefin films employed in this invention arethose ice that are prepared from poly-a-olefins having from 2 to 10 carbon atoms such as polyethylene, polypropylene, polyl-butene and the like. Polyethylene films that can be used in this invention are those prepared from so-called low density, medium density and high density polyethylene. Low density polyethylene has a density from about 0.91 to 0.929. Medium density polyethylene has a density of from 0.93 to 0.945. High density polyethylene has a density of from 0.946 to about 0.97. Films of high density polyethylene are preferred because of their high strength properties. The copolymers in the coating that is applied in accordance with the present inventionconsist mainly of ethylene, but contain at least about 5% by weight of combined secondary monomer (vinyl acetate or ethyl acrylate), and at most about 45 weight percent of the secondary monomer. Preferred copolymers are those containing from about 15 to about 30 weight percent of combined secondary monomer. lSuitable copolymers generally have densities within the range of from about 0.9 to about 0.95 gram per cubic centimeter at 25 C. Useful copolymers also must have melt indices of at least about 5 and preferably within the range of from about 10 to about 55.

Methods for preparing the copolymers that are useful in practice of this invention are well known to those skilled in the art, and the particular method by which they are made is not critical insofar as the successful practice of this invention is concerned. Nor is the particular manner in which the copolymer blends of this invention are prepared critical. For example, any of the above-described useful copolymers (having a molecular weight of at least about 10,000) can simply be blended together in a melt state in the calculated proportions. Useful copolymer blends can also be prepared by simply dissolving the proper amounts of the individual copoly- .mers in a suitable solvent. Application of the copolymer blends to the surface of a polyolefin film can be made by any of several well-known techniques such as, for example, by spraying, by dipping, and by brushing. Application of the coating can be made, if desired, by conventional roll coating techniques. Application to the film is preferably made by means of an aqueous emulsion of the copolymers, or from a solution of the copolymers in a suitable solvent. Suitable solvents for the copolymer blends of the present invention are either well known or can be readily ascertained via a simple solubility test. Such suitable solvents include (but are not limited to) toluene, xylene, cyclohexane, ethyl acetate, tetrachloroethylene, Stoddard Solvent and the like, as well as mixtures thereof.

The coated polyolefin films of this invention can be prepared by any of a number of ways. For example an aqueous emulsion of the blend of copolymers or a. solution of the copolymers in a suitable solvent system can be applied to at least one surface of the polyolefin film having the desired final thickness. Then, the volatile components of the fluid coating can simply be removed from the coated surface by conventional drying techniques. Heat can be applied to hasten removal of the solvent and/ or the water if desired. Also, the addition of heat can be utilized to increase adhesion of the resulting applied coating to the substrate. An applied powder of the copolymer blend can also be fused to the film base in this way. Note that a preferred procedure for preparing the coated films of this invention involves (a) initially the preparation of a simple mixture of aqueous emulsions of the individual copolymers,

(b) application of this mixture onto the polyolefin film surface,

(c) evaporation of the volatile components of the emulsion coating, and

Another method for preparing the coated films of the and can be readily solvent sealed to polyethylene or to M.4 cellophane, .for example, at room temperature using methyl cellosolve. In addition, the resulting coated film is nonblocking when tested at 50 C. using a method similar to ASTM D88448. Since test results by this present invention involves application of the emulsion 5 composition to at least one surface of a polyolefin film M f i system of nonblockmg and Very Shght which has a thickness greater than that desired in the ylelded'undamaged films both of Cate; final product. Subsequently, the volatile components of gones have been P together under h term PASS the emulsion are removed. The coated sheet can then be i below compression rolled by passing it, for example, between a EXAMPLE H pair of heated rolls that are rotated at substantially the Tetrachloroethylene solutions weight percent total Same p whereby the Coated sheet i reduced in h solids), of several blends f copolymers, are coated onto ness to the desired extent and there is provided a unitary conventional 1 il compression ll d high d it polymember comprising the polyolefin film having COStECl ethylene films at a rate of 1 gram of solids per quare themon a g y adherent blend of the COPOIYITIGTS meter of film. After being dried at a temperature of 100 scribed above. This rolling procedure can be accomplished C, th t d fil are t t d f th i bilit to oid either before after the Volatile Components are blocking as described above. The films are'also solvent moved from the initial Coatingsealed at room temperature with various solvents and, The particular thickness of the coatings of this inven- 20 after d y are tested for Seal Strength. Results of thes tion can be controlled fairly accurately by controlling the Various tests are listed in Table relative concentrations of the copolymer blends in the emulsions or in the solutions or in the melts that are EXAMPLE HI applied to the polyolefin sheetings and the rates at which Into 10 parts of xylene (290 F.) are dissolved 15 parts they are applied. The actual amounts of the coatings of a copolymer of ethylene/ethyl acrylate (containing (after removal of any volatile components) that have been ethyl acrylate) having a melt index of 18, along found to be useful are generally from about 0.2 to about with five parts of a copolymer of ethylene/vinyl acetate 15 grams per square meter of film surface. Preferred (containing 33% vinyl acetate) having a melt index of levels fall within the range of from about 1 to about 5 15. One part of a conventional, non-ionic alkyl acryl grams per square meter. These amounts should be applied 30 polyether emulsifyingagent and one part of a convensubstantially uniformly over the surface of the polyolefin tional wetting agent (sodium dioctyl sulfosuccinate) are film (or at least that part of the film that will be subject added to the resulting dope. The dope is stirred vigorously to the heat or solvent sealing processes). while 280 parts of hot (190 F.) water is added thereto In the following examples all parts are by weight unless over a period of about 5 minutes. The resulting emulsion otherwise specified. is then stirred continuously and allowed to cool slowly to TABLE I Solvent Seal Test Parts Parts Tetracopolymer copolymer Blocking Stoddard chloro- Cyclo- Ethyl Methyl A B test solvent ethylene hexane acetate cellosolve 3 0 FAIL PASS PASS..." PASS PASS PASS. 2 i FAIL. s s 1 5 1.5 PASS. 1 2 PASS. 0 3 PASS FAI 1 Ethylene/vinyl acetate. 2 Ethylene/ethyl acrylate.

EXAMPLE I room temperature. A 5 mil sheet of conventional poly- A mixture Comprising 105 parts of ethylene /ethy1 acry propyleneis coated onboth sides with this emulsion using late copolymer (30% ethyl acrylate) having a melt index a Y 0-036 Inch owlre wolmd -T coated of 18.5 and 35 Parts of an ethylene Him/1 acetate sheet 15 then cured at 110 C. until substantially all of polymer (33% vinyl acetate) having a melt index of 25 the. volatile materials have been evaporated, and subis stirred into a blend of 490 parts of xylene and 210 parts sefiuemly CmPres10n rolled to 1 H111 (betweeon 10 Inch of tetrachloroethylene. This mixture is then heated to o dlameter conventlqnal Steel rolls heated to 200 under about 200 F. Into the resulting solution are then dis- 3,000 pound? perhnear Inch presslire)- T fesultmsfilm solved 7 parts of a cottonseed oil monoglyceride (a can be,read11y h Sealed at 220 m a COnVFmIQmaI commercial non-ionic emulsifier), and 7 parts of a compackaglng mafihme or by means of a hafld Sealmg mercial wetting agent (sodium dioctyl sulfosuccinate). held duectlxm Contact W1th the Thls l also has The resulting hot solution is stirred vigorously while 1960 excellent reslstance t0 l gnd can readily be sol parts of hot water (200 F.) is slowly mixed into it there- Vent sefiled by {Onventlonal methods roomrtempera by forming a fairly stable emulsion. The stability of th ture Wlth a vanety of Solvents mcludmg cyclohexane emulsion is then increased by passing it through a tetrachloroethylene, Stoddard Solvent, methyl cellosolve ventional, high-pressure homogenizer while it is still hot. and ethyl acetate' Then, while it is stirred continuously, the temperature of It should be kept in mind that other materials can be the emulsion is slowly lowered to about 30 C. present in minor amounts (preferably totalling below This emulsion is then coated onto one side of 3.5 mil P t 20 Weight P in h copolymefic coatings of polyethylene film having a density of 096 gram per Cubic this invention without detracting substantially from the centimeter at a rate of about 60 grams of emulsion per 7 bemifits t Qbtamed by Practlclng the Present square meter of film. The resulting coated film is then Ventlonpassed through a conventional drying oven, followed by We 91mm! p 7 a three minute treatment at a temperature of about 110 1- A heat and Solvent scalable film comprising a poly- C. (to fuse the coating). The resulting coated film can olefin substrate and a coating on said substrate consisting be readily heat sealed at a temperatur o a ou 1 0 E essentially of a l nd of (l) a copolymer of e hy e and vinyl acetate having a melt index of at least about 5 and a vinyl acetate content of about 5 to about 45 percent by weight and (2) a copolymer of ethylene and ethyl acrylate having a melt index of at least about 5 and an ethyl acrylate content of about 5 to about 45 percent by Weight; the weight ratio of said copolymer of ethylene and vinyl acetate to said copolymer of ethylene and ethyl acrylate in said coating being in the range from about 0.3:1 to about 1:0.7 and the amount of said coating on said substrate being between about 0.2 and about 15 grams per square meter of coated surface.

2. A heat and solvent scalable film as described in claim 1 wherein said polyolefin is polyethylene.

3. A heat and solvent scalable film as described in claim 1 wherein said polyolefin is polypropylene.

4. A heat and solvent sealable film as described in claim 1 wherein said polyolefin is polyethylene, said 00- polymer of ethylene and vinyl acetate has a melt index of about to about 55 and a vinyl acetate content of about to about 30 percent by weight, said copolymer of ethylene and ethyl acrylate has a melt index of about 10 to about 55 and an ethyl acrylate content of about 15 to about 30 percent by weight, the weight ratio of said copolymer of ethylene and vinyl acetate to said copolymer of ethylene and ethyl acrylate in said coating is in the range from about 0.5:1 to about 1.121, and the amount of said coating on said substrate is between about 1 and about 5 grams per square meter of coated surface.

5. A heat and solvent scalable film as described in claim 1 wherein said polyolefin is polypropylene, said copolymer of ethylene and vinyl acetate has a melt index of about 10 to about 55 and a vinyl acetate content of about 15 to about percent by Weight, the weight ratio of said copolymer of ethylene and vinyl acetate to said copolymer of ethylene and ethyl acrylate in said coating is in the range from about 0.5:1 to about 1.121, and the amount of said coating on said substrate is between about 1 and about 5 grams per square meter of coated surface.

References Cited UNITED STATES PATENTS 3,027,346 3/1962 Rugg et al. 3,228,790 1/ 1966 Sexsmith et al. 3,285,766 11/1966 Barkis et al. 3,297,610 1/1967 Moyer. 3,399,165 8/1968 Berger et al. 3,405,083 10/1968 Morrison et al.

WILLIAM D. MARTIN, Primary Examiner J. E. MILLER, JR., Assistant Examiner US. Cl. X.R.

PO-IOSO (5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,02 Dated December 9 1969 [nventor(s) Billy R. Dotson, Edward D. Morrison and Robert F. William It is certified that error a ppears in the above-identified patent md that said Letters Patent are hereby corrected as shown below:

Column 6, line 5, immediately following "by weight," 1

insert --said copolymer of ethylene and ethyl acrylate has a melt index of about 10 to about 55 and an ethyl acrylate content of about 15 to about 30 percent by weight,--

SKSNED AND SEALED MAY 1 21970 10m ing OfflCGl iorwr of Patents 

